Molten metal injector for an injection die casting machine

ABSTRACT

A molten metal injector for use with an injection die casting machine including an injection sleeve defining an injection chamber and an injection plunger reciprocating in said sleeve, wherein the inner region of the injection chamber has a flared conical configuration terminating at its outer end in a narrow annular shoulder, and the working face of the injection plunger has a hollow cup-like extension with a thin skirt wall adapted to expand outwardly under pressure of the molten metal during injection into sealing relation with the cylindrical bore of the sleeve.

United States Patent [1 1 Miki et al.

[ Aug. 26, I975 MOLTEN METAL INJECTOR FOR AN INJECTION DIE CASTING MACHINE 3,6|3 768 lO/l97l Awano et al l64/3l2 X $685,572 8/[972 Carver et al. l64/3 l 2 FOREIGN PATENTS OR APPLICATIONS 379,702 8/ 964 Switzerland 164/312 Primary ExuminerFrancis S. Husar Axsismnt Examiner-John E. Roetliel Attorney, Agent, or FirmWilliam J. Daniel [57] ABSTRACT A molten metal injector for use with an injection die casting machine including an injection sleeve defining an injection chamber and an injection plunger reciprocating in said sleeve, wherein the inner region of the injection chamber has a flared conical configuration terminating at its outer end in a narrow annular shoulder and the working face of the injection plunger has a hollow cup-like extension with a thin skirt wall adapted to expand outwardly under pressure of the molten metal during injection into sealing relation with the cylindrical bore of the sleeve,

3 Claims, 3 Drawing Figures PATENTEB mas I915 SHEET 2 U? 2 MOLTEN METAL INJECTOR FOR AN INJECTION DIE CASTING MACHINE BACKGROUND AND GENERAL EXPLANATION OF THE INVENTION This invention relates to an improvement in molten metal injectors for use with die casting machines of the so-called cold chamber type.

A die casting machine of this type includes a composite die consisting ofa fixed die and a movable die which are joined together to define a die cavity therebetween. The molten metal to be injected is supplied to a molten metal injection chamber, formed by an injection sleeve opening into the fixed die, and then injected by the reciprocal movement of a plunger working in the sleeve into the die cavity through a narrow injection gate provided at the outlet or egress end of the injection chamber communicating with the die cavity.

In an injection casting cycle, the molten metal injected into the die cavity solidifies first along the margins which are in contact with the inner surface of the die cavity. Thus, the shrinkage holes can easily develop in the interior of the cast products because of shrinkage in the body of metal, which occurs during and as a consequence of the solidifaction of the molten metal. These shrinkage holes are undesirable because they degrade the quality of the cast products.

To avoid this disadvantage in the cast product, the injection plunger is operated in two steps in the casting cycle: in the first step, the plunger is activated to inject into the die cavity all but a selected small amount of the molten metal in the injection chamber; and in the sec ond step, which is carried out before the molten metal in the die cavity has solidified completely, the small amount of molten metal remaining in the injection chamber is injected at a higher pressure into the die cavity to achieve a supplementary metal feeding elfect, so as to prevent the development of the shrinkage holes.

In this manner cast products having minimum shrinkage holes can be obtained. However, at the end of a casting cycle any remaining molten metal solidifies and forms a biscuit, i.e., a solid metal slug, at a position adjacent to the outlet end of the injection chamber. Such a biscuit, when it is pushed by an advancing plunger for removal may cause the plunger to seize with the inner wall of the injection chamber and often impedes the free reciprocation of the plunger. This result can shorten the useful life of both the plunger and the injection sheeve because of increased wear of these elements.

Although the plunger which reciprocates within the injection sleeve is designed with a diameter almost equal to the inside diameter of the sleeve, some clear ance will remain between the plunger tip and the inner surface of the injection sleeve. Consequently, toward the end of an injection cycle when the injection pressure is very high or, especially, during the second step of the sequence of plunger operation, some of the molten metal may intrude, i.c., leak, into the clearance space between the plunger and sleeve and form a so called "casting fin" at the rear portion of the biscuit. The presence of this casting fin, together with the bis cuit, makes the reciprocating of the plunger all the more difficult. thereby not only reducing the quality of the cast products but also accelerating the wear of the plunger and the injection sleeve.

An object of this invention is to provide an improved molten metal injection die casting machine which re duces the seizure of the biscuit with the inner wall of the injection chamber during removal of the biscuit and also prevents the formation of a casting fin at the rear end of the biscuit.

Another object of this invention is to provide an improved molten metal injector which is shaped to achieve improved durability and operating efficiency in use.

In accordance with the injector arrangement of this invention the end portion of the injection chamber is formed in a flared configuration, increasing in diameter in the inward direction toward the die cavity, with a narrow shoulder being situated at the transition between the cylindrical main portion of the chamber and the flared end portion, and a thin cup-like extension projects from the margins of the face of the plunger head inwardly toward the die cavity. The outwardly flared end portion of the chamber is located adjacent to the region where the biscuit forms and serves to facilitate the removal of the biscuit by the plunger by reducing the resistance of the biscuit to ejection from the cavity in which it is formed.

Although the presence of the flared section in the chamber makes easier the removal of the biscuit, it unfortunately tends to aggravate the problem of the molten metal being forced into the clearance between the injection sleeve wall and the plunger tip during the final phase ofinjecting the molten metal into the die cavity, because it creates a wedge shaped clearance between the flared surface and the plunger periphery. According to this invention, however, a shoulder is provided at the termination of the flared section which tends to act as a barrier against the entry of the molten metal into the clearance between the injection sleeve and the plunger periphery.

In addition, the inwardly facing cup-like extension on the head of the plunger acts as a seal against the leakage of the metal into the clearance around the plunger head. The wall of this extension is relatively thin, and preferably slightly tapering so as to be radially expansible to a small degree. Hence, when the metal is under very high pressure during the final stage of injection by the plunger, the thin cup wall is elastically expanded outwardly to seal the clearance between the plunger head and the inner wall of the injection chamber. In this manner any intrusion of molten metal into the clearance between the plunger periphery and the injec tion sleeve is prevented substantially completely.

DISCUSSION OF THE DRAWINGS Now the improved molten metal injector of this invention will be described in detail with reference to the accompanying drawings, wherein FIG. 1 is a vertical section of a simplified injection die casting unit according to this invention, shown in the condition after molten metal has been loaded into the injection chamber and before injection;

FIG. 2 is a view similar to FIG. 1, but with the parts shown in their condition after the molten metal has been injected; and

FIG. 3 is a view similar to FIG. I but slightly enlarged and showing the effect of the molten metal on the novel construction of the invention at the final phase of injection.

DETAILED DESCRIPTION OF THE INVENTION In the drawings the reference numeral 1 designates a composite die consisting ofa fixed die I' and a movable die I", a die cavity 2 being formed at the junction be tween the dies I and I" when they are in closed working position.

The fixed die I is securely mounted on a stationary die plate 3 and an injection sleeve 4 extends through the supporting plate 3 with its inner end connected to the fixed die I so that the injection chamber6 within the sleeve communicates at its outlet end with the die cavity through a narrow injection gate 7 in the usual fashion of the art. Adjacent the outer end of sleeve 4 is an inlet port for introducing the molten metal to be injected into chamber 6.

An injection plunger 8 having at one end a head 9 is disposed for reciprocating movement with sleeve 4, the outer diameter of head 9 being approximately equal to the inner diameter of the sleeve. Upon advance of the plunger from the loading position seen in FIG, 1, molten metal within chamber 6 is injected into the die cavity 2.

In the extreme forward position of the injection plunger, seen in FIG. 2, a clearance space usually exists between the end face of plunger head 9 and the adjacent parts of the die, indicated at 20, and a solid metal slug or biscuit is formed in this space after injection is completed. In accordance with the invention, the region of the sleeve adjacent space 20, which will ordinarily be the outlet section of the sleeve, is flared out' wardly at 11 so that space 20 has a conical configuration, and a narrow annular shoulder I2 is provided to interrupt the transition of the tapered surface 1] into the cylindrical inner surface of sleeve 4.

The face of the plunger head 9 is rather deeply recessed to form a hollow cup-shaped extension 14 projecting from the otherwise solid head and the walls of the cup are made sufficiently thin as to be expanded elastically by the pressure of the molten metal during the final phase of a casting cycle.

In operation, during injecting, the plunger head 9 proceeds rapidly past the position shown by the dotted line to the position shown by the solid line (FIG. 3), and the presence of the shoulder 12 creates strong resistance to the backward flow of the molten metal and easily prevents the molten metal I0 from leaking into the clearance between the injection sleeve 4 and the periphery of plunger head 9. Absent this shoulder, the molten metal 10 would tend to flow into said clearance through the wedge-shaped space formed between the tapered wall 11 and the plunger periphery 9. In the sec 0nd stage of injection toward the end of a casting cycle, when the pressure of the molten metal 10 increases to its maximum, the provision of the thin-walled cup-like extension 14 at the working face of plunger head 9 sets up an almost perfect seal between the plunger head 9 and the bore of the injection sleeve 4. This is because the pressure of the molten metal 10 acting against the plunger face 14 presses against the thin skirt wall I3 of extension 12 in the direction of arrows (FIG. 3) and the thin skirt wall 13 is expanded elastically into a sealing relation with the bore of injection sleeve 4. According to this embodiment, the molten metal 10 can be prevented most advantageously from flowing into the clearance between the plunger tip 9 and the injection sleeve 4 by adjusting the volume of molten metal retained in injection chamber 6 by adjusting the final position of plunger head 9. Thus, at the end of an injection operation, the extreme end or tip of the plunger extension 14 can be located at any point between a position in registration with the shoulder I2 at the base of the tapered wall 11 and a position projecting by about 15 mm inwardly from the shoulder 12, as shown in FIG. 2.

When the casting cycle is finished and the die is opened to remove the cast product, the flared or conical configuration 11 of the biscuit-forming region of the injection chamber assists in the easy removal of the solid metal biscuit since the resistance of the biscuit in sliding free of this region is minimal.

Our experiments show that the preferred inclination of the flared wall II is within the range of an angle of 2 to 7 to the central axis of injection sleeve 4 and that the radial thickness of the shoulder 12, although varying somewhat depending on the inner diameter of injection sleeve 4, must be at least one one-hundredth of the inner diameter of the injection sleeve 4 or, when an injection sleeve 4 having an inner diameter of mm is used, for example, it must be more than 1 mm. The length and thickness of the thin skirt wall I3 of cupshaped extension I4 varies depending upon the injection force of the casting machine, the inner diameter of the injection sleeve 4 and the material of construction of the plunger head 9. When the plunger head 9 is made of an ordinary material, such as low-carbon alloy steel or high-speed tool steel, the thin skirt wall I3 should preferably be 7 30 mm long, i.e., in the axial direction, and 5 15 mm thick at the base thereof. Wall I3 should taper so that it is increasingly thinner toward its free end.

It will now be understood that significant disadvantages in conventional die casting machines are removed by the molten metal injector of this invention, which makes possible an effective and stabilized casting operation for an extended period of time, Furthermore, the molten metal injector of this invention has a simple structure, simplifying its manufacture and operation,

and operates efficiently to produce precision cast products.

What is claimed is:

I. In an injection die casting machine including fixed and movable dies defining a die cavity, an injection sleeve in communication at its inner end with said cavity for receiving into the bore thereof molten metal for injection into said cavity, and a plunger arranged for reciprocation in said sleeve and operable to inject said molten metal, in combination, the improvement comprising a cavity at the inner end of the injection sleeve, in coaxial relation to said sleeve, in which cavity is formed a slug of solid metal after injection, the periph eral wall of said cavity being of conical configuration flaring away from said sleeve to facilitate removal of the slug from such cavity at the end of the injection cycle, said cavity terminating at its smaller end in a narrow annular shoulder whereby backward flow of metal into the clearance between plunger periphery and sleeve bore adjacent said inner end of the sleeve is resisted.

2. The die casting machine as in claim I, wherein said flared cavity wall is inclined at an angle of about 2 7 to the sleeve axis.

3. The die casting machine of claim I wherein said annular shoulder has a radial dimension equal to at least about one one-hundredth of the diameter of the bore of the injection sleeve, 

1. In an injection die casting machine including fixed and movable dies defining a die cavity, an injection sleeve in communication at its inner end with said cavity for receiving into the bore thereof molten metal for injection into said cavity, and a plunger arranged for reciprocation in said sleeve and operable to inject said molten metal, in combination, the improvement comprising a cavity at the inner end of the injection sleeve, in coaxial relation to said sleeve, in which cavity is formed a slug of solid metal after injection, the peripheral wall of said cavity being of conical configuration flaring away from said sleeve to facilitate removal of the slug from such cavity at the end of the injection cycle, said cavity terminating at its smaller end in a narrow annular shoulder whereby backward flow of metal into the clearance between plunger periphery and sleeve bore adjacent said inner end of the sleeve is resisted.
 2. The die casting machine as in claim 1, wherein said flared cavity wall is inclined at an angle of about 2* - 7* to the sleeve axis.
 3. The die casting machine of claim 1 wherein said annular shoulder has a radial dimension equal to at least about one one-hundredth of the diameter of the bore of the injection sleeve. 